Effect of Bacillus thuringiensis (Bt) Cryl Ac toxin and protease inhibitor on growth and development of Helicoverpa armigera (Hubner)

Adaptation of insects to plant protease inhibitors and development of resistance to Bacillus thuringiensis (Bt) insecticidal toxins has been laid the concept of combination of different insecticidal proteins. While using the combination of insecticidal proteins, it is important to have complete understanding of the target insect physiology and midgut biochemistry. In the present investigation, we report the combined effects of Bt Cry1Ac toxin and protease inhibitor (PMSF) on the growth and activities of midgut digestive proteases of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae). We also checked the interactions between H. armigera midgut soluble aminopeptidases and Bt Cry1Ac toxin. As expected, the larval growth and survival was found to be reduced on the diets supplemented with Cry1Ac and PMSF as compared to control larvae. Significant reduction in the growth and survival rate of the larvae was observed on the diet incorporated with the combination of Cry1c and PMSF. H. armigera midgut soluble aminopeptidase activity was strongly decreased in the larvae reared on Cry1Ac as compared to larvae fed on control diet. Serine proteinase activities were significantly declined in the larvae reared on PMSF containing diet as compared to control larvae. However, the serine proteinase activities were notably increased in the larvae fed on Cry1Ac. Reduction in the aminopeptidase activity with LpNA in the H. armigera larvae was compensated with an induction of aminopeptidase activity with ApNA. Our findings could be helpful to further dissect the roles of midgut soluble aminopeptidases in the perception of Bt toxins. Studies also suggest that combination of different types of insecticidal proteins such as Bt Cry toxin and protease inhibitors might be a promising pest management strategy.(C) 2013 Elsevier Inc. All rights reserved.